Supercooling is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid. A liquid crossing its standard freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form creating a solid.
Freezing is almost always an exothermic process, meaning that as liquid changes into solid, heat and pressure are released. This is often seen as counter-intuitive since the temperature of the material does not rise during freezing, except if the liquid were supercooled. But this can be understood, since heat must be continually removed from the freezing liquid or the freezing process will stop. The energy released upon freezing is a latent heat, and is known as the enthalpy of fusion and is exactly the same as the energy required to melt the same amount of the solid.
Lacking any such nuclei, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs. Homogeneous nucleation can occur above the glass transition temperature, but if homogeneous nucleation has not occurred above that temperature an amorphous (non-crystalline) solid will form.
Water normally freezes at 273.15 K (0° C. or 32° F.) but it can be “supercooled” at standard atmospheric pressure (15 psi) down to its crystal homogeneous nucleation at almost 224.8 K (−48.3° C./−55° F.). The process of supercooling requires that water be pure and free of nucleation sites, which can be achieved by processes like reverse osmosis, but the cooling itself does not require any specialised technique.
The melting of a solid above the freezing point, which is the opposite of supercooling, is much more difficult, and a solid will almost always melt at the same temperature for a given pressure. For this reason, it is the melting point which is usually identified, using a melting point apparatus; even when the subject of a paper is “freezing-point determination”, the actual methodology is “the principle of observing the disappearance rather than the formation of ice”.
Supercooling is often confused with freezing-point depression. Supercooling is the cooling of a liquid below its freezing point without it becoming solid. Freezing point depression is when a solution can be cooled below the freezing point of the corresponding pure liquid due to the presence of the solute; an example of this is the freezing point depression that occurs when sodium chloride is added to pure water.
Refrigerated glass-door beverage merchandisers have been used for many years to keep beverages chilled below room temperature yet above the freezing point of water (32 deg-F, 0 deg-C). In recent years, several beverage merchandiser manufacturers have introduced special refrigerated merchandisers (super-chillers) for beer and other alcoholic beverages that chill these items below the freezing point of water, with advertised chilling temperatures as low as 22-28 deg-F (−5.5 to −2 deg-C). Manufacturers claim these lower storage temperatures are possible due to the alcohol content of these beverages which lowers their freezing point (freezing point depression). These sub 32 deg-F storage temperatures are generally considered beneficial for beers and alcoholic beverages since the flavor is colder and the beverage stays colder longer during consumption than when stored above 32 deg-F. However, these new alcoholic beverage merchandisers generally do not allow storage temperatures below 22 deg-F (−5 deg-C) since the freezing point of most beer is between 24-28 deg-F depending on specific alcohol content. Thus the current temperature ranges generally available for commercial beverage merchandisers are between 22 deg-F and 50 deg-F (−5.5 to +10 deg-C).
One commercial application of supercooling is in refrigeration. For example, there are freezers that cool drinks to a supercooled level so that when they are opened, they form a slush. The SLUSH-IT!™ drinks mixer system uses stickers placed on the beverage which is then placed into a specially designed receptacle. The receptacle is then placed in a standard freezer. Another example is a product that can supercool the beverage in a conventional freezer. The Coca-Cola Company also briefly marketed special vending machines containing Sprite in the UK, and Coke in Singapore, which stored the bottles in a supercooled state so that their content would turn to slush upon opening. This system, however, requires the use of a specially designed bottle.
Thus, it has been known that non-alcoholic bottled and canned beverages of all varieties, including bottled water, can be supercooled below 32 deg-F (0° C.) while remaining liquid for short periods of time regardless of the various types of ingredients. What is not generally known is how to store these beverages indefinitely in a supercooled liquid state without allowing them to freeze solid.
When supercooling beverages, the liquid beverage is sensitive to temperatures even a few degrees below the set point which is a temperature within a range below the freezing point of the liquid and above the solid phase transition temperature. The sensitivity of a supercooled liquid beverage to temperatures below the set point can cause the liquid to nucleate inadvertently and begin to freeze.
A prior art reference, Chung et al., U.S. Pat. No. 8,572,990, discloses an apparatus for supercooling which stably maintains a liquid in a supercooled state below a phase transition temperature by mounting temperature sensors directly to tops of each container (i.e., such as a bottle) and applying energy to the surface of the liquid or contents or to a gas near the surface while the liquid is maintained in the supercooled environment.
The prior art references do not acknowledge and address one specific problem that occurs in the supercooling of liquids which is the fact that liquids held below a freezing point can and do inadvertently begin ice nucleation and freezing. The nucleation can have a domino effect meaning that several closed containers will begin to freeze.
Since a frozen can or bottle is undesirable in a supercooler; there is a need for a user-interactive method or system to obviate this condition and prevent inadvertent nucleation of supercooled liquids as provided by the present invention without mounting sensors directly to tops of the containers.
The present invention also contemplates a standard refrigerator that is customized to contain a supercooler unit or compartment and a slush activation device. The supercooler unit or compartment includes a user-interactive method or system of the present invention to warn and alert a user thus alleviating concerns for the inadvertent freezing of supercooled liquids stored in closed containers inside the refrigerator. The slush activation device is located in the front door of the refrigerator to safely and conveniently create a slush, icy beverage or drink in the home environment.